From a1fd7794e783c5f315af8654cf9f744af0663c0a Mon Sep 17 00:00:00 2001
From: a <a@tuxpa.in>
Date: Sat, 26 Mar 2022 14:16:31 -0500
Subject: [PATCH] wip

---
 filter.go | 12 ++++++++++++
 fold.go   |  9 +++++++++
 go.mod    |  3 +++
 map.go    | 33 +++++++++++++++++++++++++++++++++
 4 files changed, 57 insertions(+)
 create mode 100644 filter.go
 create mode 100644 fold.go
 create mode 100644 go.mod
 create mode 100644 map.go

diff --git a/filter.go b/filter.go
new file mode 100644
index 0000000..1be680f
--- /dev/null
+++ b/filter.go
@@ -0,0 +1,12 @@
+package lambda
+
+func Filter[T any](xs []T, fx func(T) bool) []T {
+	n := 0
+	for _, x := range xs {
+		if fx(x) {
+			xs[n] = x
+			n++
+		}
+	}
+	return xs[:n]
+}
diff --git a/fold.go b/fold.go
new file mode 100644
index 0000000..3981d5c
--- /dev/null
+++ b/fold.go
@@ -0,0 +1,9 @@
+package lambda
+
+func Foldl[T any](xs []T, fx func(T, T) T) T {
+	return *new(T)
+}
+
+func Foldr[T any](xs []T, fx func(T, T) T) T {
+	return *new(T)
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..2dba43e
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module git.tuxpa.in/a/lambda
+
+go 1.18
diff --git a/map.go b/map.go
new file mode 100644
index 0000000..562fae4
--- /dev/null
+++ b/map.go
@@ -0,0 +1,33 @@
+package lambda
+
+func Map[T any](xs []T, fx func(T) T) []T {
+	for i, v := range xs {
+		xs[i] = fx(v)
+	}
+	return xs
+}
+
+func MapV[T, V any](xs []T, fx func(T) V) (ov []V) {
+	ov = make([]V, len(xs))
+	for i, v := range xs {
+		ov[i] = fx(v)
+	}
+	return
+}
+
+func MapError[T any](xs []T, fx func(T) (T, error)) (ov []T, oe []error) {
+	oe = make([]error, len(xs))
+	for i, v := range xs {
+		xs[i], oe[i] = fx(v)
+	}
+	return
+}
+
+func MapErrorV[T, V any](xs []T, fx func(T) (V, error)) (ov []V, oe []error) {
+	ov = make([]V, len(xs))
+	oe = make([]error, len(xs))
+	for i, v := range xs {
+		ov[i], oe[i] = fx(v)
+	}
+	return
+}